Conventionally, there have been well known techniques of an actuator having a diaphragm dividing an inside of a casing into a negative pressure chamber and an atmospheric pressure chamber, a plate provided inside the negative pressure chamber to contact with the diaphragm, and an operating shaft which is capable of being displaced in the axial direction according to the deformation of the diaphragm, for example, as disclosed in Patent Literature 1.
An actuator disclosed in Patent Literature 1 includes a diaphragm dividing an inside of casings (a first case and a second case) into a negative pressure chamber and an atmospheric pressure chamber, a plate (a diaphragm receiving plate) provided inside the negative pressure chamber to contact with the diaphragm, and an operating shaft (an output member) capable of being displaced in the axial direction according to the deformation of the diaphragm.
With this configuration, the actuator disclosed in Patent Literature 1 causes deformation (movement) of the diaphragm by changing pressure inside the negative pressure chamber, and thereby the operating shaft is displaced in the axial direction. Further, the actuator disclosed in Patent Literature 1 is capable of causing deformation of the diaphragm while maintaining a predetermined shape (specifically, a planar shape at the center) by the plate.
However, the actuator disclosed in Patent Literature 1 is formed such that the plate partially projects from the negative pressure chamber to an inside of the atmospheric pressure chamber through a through hole provided in the diaphragm. Thus, in the actuator disclosed in Patent Literature 1, the plate contacts with the atmosphere, and thereby strength of the plate may be decreased due to hydrolysis.